21 Tips to Perfect Exhaust Design

21 Tips to Perfect Exhaust Design

Exhaust systems have a simple job - they take the spent exhaust gasses away from the engine. The best type of system is the one with the least number of bends and with an efficient muffler designed to reduce drone and noise. For anyone new to exhaust performance topics, here are a few guidelines that can help you avoid some of the most common errors made by exhaust builders.

#1 Exhaust is not fluid.

While the spent exhaust gasses that exit your tail pipe appear to be fluid, they are in fact a series of pulses. Just think for a moment how the exhaust is created. Hot exhaust gasses exit the combustion chamber/cylinder exhaust valve has opened to let them out. The exhaust valve then closes and another combustion cycle occurs creating subsequent "bursts" of exhaust gasses.

#2 The Simpler the Better

The fewer the number of bends in the exhaust system, the better it will perform. It just makes sense - a shorter, smoother route to the tail pipe is better when possible.

#3 Correct Exhaust Exit

Your exhaust system must exit well past the passenger compartment of the vehicle. This is the very minimum. If the exhaust does not extend at least a foot past the interior, the exhaust gasses can enter the vehicle compartment. News flash - exhaust gas contains carbon monoxide - a deadly, colorless poison. Extend the exhaust system out and away from the vehicle interior.

#4 Correct Exhaust Direction

On vehicles that either tow a travel trailer or station wagons that have rear facing rear windows, the exhaust should be directed out and away from the rear of the vehicle. Exhaust gasses can curl up behind the rear of the vehicle and enter the trailer or into the back window of the vehicle. Exhaust systems that direct the exhaust gases to the side of the vehicle behind the rear tires is recommended.

#5 Exhaust Header Legality

Exhaust headers negatively affect the emissions output of the vehicle but scavenging exhaust gas away from the engine in larger amounts than factory exhaust manifolds. Headers are great for performance applications, but are not legal in states where emissions adherence is necessary.

#6 Shorty vs Full Length Headers

Exhaust headers come in two forms in most applications - shorty and full length. Only full-length headers provide an overall horsepower increase. Shorty headers can often keep the vehicle within emission standards, but they offer no real performance benefit.

#7 Tune your engine after you add full-length exhaust header.

Your vehicle will now allow the engine exhaust gasses to flow out of the engine more freely which means it can benefit from increased fuel and intake air flow. Achieve all the performance benefit you can by tuning the fuel system and making ignition timing adjustments.

#8 Headers can be too big.

Headers are measured in terms of overall length, primary tubing (the smaller diameter tubing at the top) and collector tubing (the tubing after the primary tubes merge down below). If the primary tubing is too larger for your engine, it can cause performance to diminish along with drivability. Research the correct header configuration for your engine before you install them.

#9 Tubing Sizes

You can go too big with the diameter of your exhaust tubing and end up with diminished performance. While most performance exhaust kits will have selected the optimum cat-back tubing size for your engine, it is good to know what you are working with. For engines in the 200-450 horsepower range, a 2.5-inch diameter exhaust tubing is recommended. Under 200hp, a 2.25-inch tubing will work and over 450 horsepower, a 3-inch diameter tubing is suggested.

#10 Mandrel bends are better than compression bends.

Mandrel bends are denoted by a smooth consistent bend in the tubing. This is accomplished by using a mandrel bender that inserts a mandrel inside the tubing while shaping the tube to keep the tubing from crimping. A compression bender is denoted by a series of folds on the inside edge of the bend. Compression bends slow the flow of exhaust gas inside the tube and reduce performance.

#11 Use of the Same Hangers

A quality performance exhaust will use the same exhaust hangers as the factory exhaust. Your vehicle was designed at the factory after hours of engineering time was spent to build the best possible vehicle. Utilizing the same hangers will keep exhaust away from fuel lines, suspension parts and fuel tanks. The only exception to this is when you are replacing a single exhaust with a dual system. In this case, you should be careful to make sure all parts avoid sensitive areas.

#12 Proper Installation

When installing a performance exhaust, there is always a need for adjustment. For this reason, exhaust kits should be installed with all the clamps only lightly tightened so the parts can be adjusted. It is very common to have to adjust the system a couple of times while inserting parts deeper at coupling points or to turn the tubing to improve the fit. But never allow any exhaust tubing to come in contact with a chassis part or fuel line or hang down where it can catch on road debris.

#13 Rack Use When Installing

Install your exhaust on a rack that keeps the compression compressed rather than handling down. This may not be your call, but the best vehicle lifts for suspension installation are the kind with the ramps that keep the vehicle at ride height rather than dangling. If you use the latter style of lift, when the vehicle is brought back tor the ground, check carefully for any contact points or fuel line proximity issues.

#14 Aluminized vs Stainless Steel.

For years, aluminized exhaust was all there was in terms of aftermarket exhausts. This lightly coated galvanized metal had a short life in most cases, the tubing ultimately rusting and falling apart. Vehicle manufacturers heard the cries of many vehicle owners and switched to stainless steel in the early 1990's virtually eliminating aluminized exhaust. Stainless steel exhaust is the only way do go despite the slightly higher price. Note that 409 stainless steel is the most common stainless used for exhaust because it can be bend easily to the shapes required, but it will pick up a brown discoloration after a short time. This may alarm some owners. Not to worry, it is just a surface discoloration and it will not rust through.

#15 Proper exhaust tubing clamps are imperative.

As noted earlier, exhaust gas leakage can be deadly. A correct clamp will apply force all the way around the connection rather than at any one point and tighten with enough force to remove any chance of leakage. Never use hose clamps, or any other type of non-exhaust clamp, to join exhaust tubing together.

#16 A balanced system is best.

By this we mean that if you have a dual exhaust system with twin rear tips, the exhaust should have a point where they share gasses. In some kits this can take place within the muffler itself (where the main three inch exhaust enters the muffler and then splits into two rear exit tubes). With custom exhaust systems, an X or H-pipe will help balance the two sides of the system.

#17 X and H-pipes can make your exhaust emit higher or lower tones.

An X-pipe, where the two sides of the exhaust system cross in an X shape, will emit a higher final exhaust pitch than an H-Pipe (a pipe that runs perpendicular to the two rear exhaust tubes) which will create a lower final exhaust tone.

#18 Tubing Should Not Butt Together

Exhaust tubing should slip one inside the other rather than butting tubing together. Tubing should overlap to create a leak-free joint. On a qualify exhaust kit, one tube will be slightly smaller in diameter than the other allowing the tube to overlap at least 2.5-inches. The clamp should then slide over the overlapped section with at least one inch between the edge of the clamp and the end of the outer tube.

#19 Use an Isolator

Always use an isolator between the factory body hanger and the exhaust system. This isolator, made from either rubber or phenolic plastic, keeps the exhaust vibrations from transferring to the vehicle chassis. Never use wire ties to hang exhaust and install the retaining "keepers" included in the kit on the hanger rod ends to stop them from sliding off.

#20 Dented tubing is restrictive.

Should your exhaust come is contact with road debris or the road, it can be damaged by denting. At the point of impact two things happen - first, the tubing is now smaller than design reducing airflow and second, there is potential for a tubing puncture at some point. A qualified exhaust technician using the same size and quality tubing should replace the damaged area.

#21 Use common sense.

Exhaust is not rocket science. The object here is to keep the dangerously toxic exhaust gasses from entering the passenger cabin. If there is any area where exhaust can leak out, close that hole or reroute the exhaust out and away. Common sense is key here. 

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